Cantharidus dilatatus

Lore & Background

The shell grows to a length of 8 mm, with a diameter also of 8 mm. It is small, imperforate, and conical in shape, with spiral striae that are numerous, fine, and inconspicuous, becoming more distinct and a little further apart on the base. The colour is cinereous, pink, or pinkish-brown, usually with white markings near the suture or tessellated with white. Sometimes a broad dark-brown band encircles the periphery of the whorls, and one on the centre of the base. White zigzag bands sometimes adorn the last two or three whorls. The epidermis is thin, slightly shining, and easily worn off.

The spire is conical, as high as the aperture and a little convex. The apex is acute. The protoconch is very small, consisting of 1½ smooth, slightly convex whorls. The six whorls are slightly convex. The body whorl is obtusely angled at the periphery and considerably expanded. The base of the shell is flat. The sutures are linear, but little impressed. The aperture is subrotund, oblique, inside mostly highly bluish-reddish iridescent and finely lirate. The outer lip is strengthened by an inner white callosity. The concave columella is vertical. The inner lip is broadly expanded, covering the umbilicus, and spreading as a broad white callosity over the parietal wall.

Reader's Guide

This species is documented in the New Zealand Recent species revision of Cantharidus by B.A. Marshall (1998), and appears in standard references such as Powell's New Zealand Mollusca (1979) and Miller & Batt's Reef and Beach Life of New Zealand (1973). Its significance lies in its endemic status to New Zealand, occurring off the North, South, Stewart and Chatham Islands. The detailed description of its shell—including its variable colour patterns, fine spiral sculpture, and iridescent aperture—provides a clear basis for identification within the Trochidae family. The species is known only from these sources, and no further ecological or behavioral data are given in the article.